3.9 V8 EFI Driving me mad

ukspeedtraps · Post by **ukspeedtraps** » Thu Dec 15, 2011 9:21 pm

Hi I have been searching for a month for answers and was told to come on here by my Bro in Laws son.., Sorry if this has been asked before.

I have a Range Rover Classic V8 3.9 with 14CUX ignition.

The problem I have is that it will run from start up on tick over no problem, if I push the accelerator down hard it will drop in rpm almost to the point in stalling, a few seconds later it will rev up no problem. If I put it into drive and pull away it will stall and not pull away unless I feather the revs up to quite high and then it will move but then as soon as i take my foot off the throttle it will cut out.

It appears to be over fueling as I get rather good flames out of the exhaust See, http://youtu.be/nXGGXw0gzQc it gives you an idea on how its running.. 0.16 seconds is it ticking over after a rev. (Thank god for a stainless exhaust)

I have cleaned and tested the stepper motor, replaced the fuel temp sensor, water temp sensor, new MAF (not orignal LR Part), new leads (last year), new spark plugs, new TPS

Its on a 1 year old rotor arm and dizzy cap.

Its always run just great until the TPS failed. It was replaced with a Britpart TPS.

I plan to restore the Classic starting in spring, but really need it running before that.

At that point the options are to keep the 14CUX, Replace it with carbs or a Meggasquirt system.

In the meantime has anyone please got any suggestions.

I am based in Burton upon Trent, Can't take it to a dealer as its now SORN (Tax was up in Nov so not point until I get it running) and unsafe to drive with this problem.

Please help

PS I am technical but no mechanic, and learning fast..

Post by **Coops** » Thu Dec 15, 2011 9:38 pm

HI and welcome,
was it Jairm that pointed you this way

have you tried another tps unit?
wondering if the wiring maybe different on the current tps that your using.

ukspeedtraps · Post by **ukspeedtraps** » Thu Dec 15, 2011 10:04 pm

Yep, Jairm is the guilty one.

I have had three of them so far, the one I had was a replacement to the LR one that packed ii 110000 miles then a Britpart one, 4000 miles, then a new one that was faulty to start and this one I have now..

I have checked the wiring, its the same, I read somewhere that the TPS can have some play in it that allows the wiper arm to move and one chap added a shim to push the arm on better. I have not tried this yet but will give it a go.

I am not convinced either way if its the TPS, I have run the engine with the old TPS disconnected and the problem I have was not there so I dont think it is, but not being to well informed on engines and the problems its all trial and eror for me.

Post by **Coops** » Thu Dec 15, 2011 10:17 pm

limp mode?
i think if the ecu goes into limp mode it runs rich,

maybe one of the guys can confirm this,
has it got lambda sensors in the exhaust?
wondering if one of these is failing?

ukspeedtraps · Post by **ukspeedtraps** » Thu Dec 15, 2011 10:41 pm

Yes it has lambda sensors the cats have been removed though and a straight through added. It has done 10k on the new exhaust with no issues.

Not sure how to test them though. I will check the wiring though to make sure its not broke

Would limp mode kill the engine so badly though

Ian Anderson · Post by **Ian Anderson** » Fri Dec 16, 2011 9:02 am

Yes it does

To get it out of limp mode
Disconnect battery for 30 seconds plus - to let residual current ebb away
Reconnect - limp mode removed

Damn - I even have a master key fitted to my battery lead so I can reset it with no tools

Ian

DaveEFI · Post by **DaveEFI** » Fri Dec 16, 2011 9:26 am

What voltage do you get measuring from the TPS yellow to engine block? And TPS yellow to red/black? That should show if the reference voltage the ECU outputs to sensors is correct, and if there are grounding issues. Probe the TPS connector back while it is plugged in.

ukspeedtraps · Post by **ukspeedtraps** » Fri Dec 16, 2011 7:31 pm

I will drag her out of the garage try the above in the morning

ukspeedtraps · Post by **ukspeedtraps** » Sat Dec 24, 2011 1:10 pm

Never got round to doing this I am off new for a week so will have a play with her. Disconnecting the battery for two days made no diference though.

shaunod · Post by **shaunod** » Tue Jan 03, 2012 10:12 pm

I would test the following;
1) TPS Voltage - as Dave suggested - but between the centre wire on the TPS (usually green) and the red wire (should be ECU Ground). You are looking for a voltage of .32V at no throttle, rising smoothly as you open the throttle until it reaches about 5V at wide open throttle.
2) Fuel pressure regulator - mounted on the back of the fuel rail, should have a vacuum hose connected to the stepper motor housing make sure it is not split and connected both ends.
3) Check the timing - take the vacuum off the dissy ... the pipe that is ... look for about 26 degrees BTDC at 3500 rpm .. don't worry too much what it reads at idle .. just as long as it is moving back around 15 or 20 degrees. Re-connect the vacuum and see what it reads at idle, as long as the vacuum is advancing it substantially it will be okay.
4)Check that the inlet hose - between the plenum and the airflow meter - has no splits or leaks.

That should do for starters.